Starting from a text-to-speech conversion programme (Carlson and Gran- strom, 1975), a note-to-tone conversion programme has been developed (Sundberg and Fryden, 1985). It works with a set of ordered rules affecting the performance of melodies written into the computer. Depending on the musical context, each of these rules manipulates various tone parameters, such as intensity level, fundamental frequency, and duration. In the present study the musical effect of nine rules is tested. Ten melodies were played under several rule-implementation conditions, and musically trained listeners rated the musical quality of each performance. The results support the assumption that the musical quality of performances is improved by applying rules.